A known technique of manufacturing battery plates involves the punching of a grid of openings in a strip of lead sheeting, and the filling of the grid openings with a material in paste form prior to the cutting or punching of the plate out of the strip.
This technique is encumbered with several disadvantages which can seriously affect the quality of the finished plates, and which additionally can severely curtail the useful life of the cutting dies or punches required in the cutting or punching of the plates out of the strip.
In particular, the paste which is filled into the grid openings is a highly corrosive material comprised of lead powder, lead oxide, lead sulfate and water, which, when filled into the openings spreads over the surrounding area of the lead strip, and, during the subsequent die cutting or punching operation to remove the filled plate from the lead strip, contaminates the cutting die or punch and results in the rapid corrosion thereof.
As cutting dies or punches formed from high-speed steel or die steel are readily susceptible to corrosion by the paste, it has been found necessary to resort to cutting dies or punches formed from a corrosion resistant material, such as a cobalt alloy.
While the use of this expensive alloy extends the useful life of the cutting die or punch, it still is not entirely satisfactory, in that corrosion of the cutting die or punch still proceeds, but at a lower rate, and results in the ultimate destruction of the die or punch in an extended but still a relatively short time.
In an attempt to further extend the useful life of the cutting die or punch, resort has been made to the coating of the die or punch with a ceramic material. Such materials are, however, inherently brittle and friable, and upon wear of the coating expose the metal substrate to the corrosive paste, this resulting in etching of the substrate and the rapid breakdown of the then unsupported ceramic coating.
Additional problems which arise in this manufacturing technique are that of distortion or deformation of the filled plate as it is struck out of the stock strip material, and, the displacement or falling out of the paste material under the impact shock of the punching operation, both of which militate against the continuous production of uniformly high quality plates of close manufacturing tolerances, and result in an increase in the number of rejects in a production run.
In an attempt to avoid these problems, it has been prior proposed to punch the entire plate blank and remove it from the stock strip material prior to the filling of the grid openings with the paste material. Such an operation, however, carries with it the disadvantages that additional machinery is required in the handling of the individual plates, and a high production rate cannot readily be achieved.